Photographic light-sensitive material containing selenium and process of making the same



' Patented Oct. 12, 1926.

' UNITED STATES v 1,602,592 PATENT OFFICE.

SAMUEL E. SHEPPARD, OF ROCHESTER, NEW YORK, ASSIGNOR TO EASTMAN KODAK COMPANY, ROCHESTER, NEW YORK, A CORPORATION OF NEW YORK.

PHOTOGRAPHIC LIGHT-SENSITIVE MATERIAL CONTAINING SELENI'UM AND P ROCESS OF MAKING THE SAME. V i

No Drawing. Original application filed June 6, 1924, Serial No. 718,411. Divided and this application filed January 21, 1926. Serial No. 82,847.

This application is a. division of my prior Patent Number 1,574,944, dated March 2,

1926, granted on application No. 718,411,

filed June 6, 1924 for photographic light sensitive materials and processes of making the same. i

This invention relates to the art of photographic materials.

One object of the invention is to provide photographic emulsions, especially developing-out ones, having new or improved properties because of the use or presence therein of materials, the sensitizing properties of which I have discovered. Still another object of my invention is to provide processes in "which such materials are used to improve photographic emulsions, especially developing-out ones, as regards light-sensitiveness,

v by which term I include their ability to give the earliest visible impression or image with the minimum exposure or their ability to giy e density after a given exposure or both, the usual photographic fluid treatments being used in preparing such impression or image or density.

A further object of the invention is to provide colloid products, such for instance as gelatins, the usefulness of which for forming light sensitive photographic emulsions, especially developing-out emulsions, is greatly increased and controlled by my said sensitizing materials incorporated therewith. Another object of the invention is to provide processes for preparing said colloid products or intermediates. 7

.Other objects are,'to increase the sensi' tiveness of photographic emulsions, especially developing-out emulsions, while Whol, ly or partially dispensing with expensive or 40 long and'uncertain so-called ripening methods; to enable the use of a type of gelatin having desirable physical qualities in mak ing such aphotographic emulsion of greater light-sensitiveness than that normally obtainable with said gelatin; to obtain more stable emulsions through the purity of the ingredients; to increase the dight-sensitiveness ofphotographic emulsions, particularly developing-out ones, the grain characteristicg of which have already been determined; to increase the general light-sensitiveness of such photographic emulsions throughout the spectral ranges to which compounds produce remarkable light-sensitizing effects upon photographic emulsions, especially developing-outlones when incorporated therein. Broadly speaking each compound ofthese series contains a divalent selenium atom which is joined by a double bond to a single metalloid atom (not one .bond to one atom, and the other bond to a different atom) to which at least another group of atoms is attached. 'Generally it is desirable thatthe last mentioned group of atoms be such that it induces 1n the compound a chemical afiinity for silver ha1ids,

for instance the compound may combine to an appreciable extent with silver halidto form a soluble complex salt, when said atomic group'is present. Moreover, the inetalloid atom to which the atom of selenium is joined by a double bond is in many instances, but not necessarily, a carbon atom.

For some of the preferred examples of myinvention, I select from-the above series the following subseries selenocarbamids. As the corresponding carbimids are likewise usable in preferred examples of my invention and are readil changed into said carbamids, especially 2hr instance in emulsions of the alkaline or ammonia type, it will be understood that the corresponding car'bimids are included hereinafter when said carbamids 1 I are'claimed. These subseries of carbamids and carbimids include many compounds containing one ormore substituent radicals, such as alkyl,aryl, acyl, alkyl-oxy, a'ryl-oxy, etc., groups. Examples are allyl isoselenocy anate, allyl selenourea. Not only can each compound of my series of light-sensitizers be used alone to improve an emulsion (or Cll0ld for an emulslon) but two or more of such compounds may be used together to obtain their mutual or cumulative effects.

It is a common characteristic of the compounds which I'nse, that said double bonded the sulfur atom in ethyl mercaptan for example. Consequently said double bonded sulfur-group atoms in my compounds corres and roughly in the firmness with which t e are held to the firmness with which the sulfur atoms areheld in the so-called potential mercaptans, although there is, of course, some range of difference in the firmness with which said double-bonded atoms are held in the diflerent compounds of my series. The

sensitiveness of the grains of silver halid in emulsions has been shown to correspondto the presence in said grains of nuclei of unstated chemical composition. I, therefore, attribute the sensitizing action of my compounds to their forming in the emulsion grains small, mostly ultramicroscoplc, nuclei which include silver combined with selenium. The intermediate firmness with which said double-bonded atoms are held in my compounds facilitates this scattered formation or reaction without reacting on the whole of each grain. Since this deduction is not indispensable to the practical using of .my invention, I do not wish to be limited to it except as defined in the claims.

I have also found that the proportions in which my compounds are incorporated in the emulsions 'or in the colloids for the emulsions) are important. If used in too high concentrations, they cause fog, and sometimes reversal. The largest proportions which can be effectively used yary somewhat with the articular sensitizing compound or compoun s which are used, w1th the proportion of gelatin to silver halid in the emulsion, with the type of emulsion as regards gra n size characteristics and alkalinity, with the amount of natural sensitizer originating in the gelatin when the latter is manufactured,

with the particular silver halid or halids' employed, the standard. as regards fog which is set by the emulsion maker, etc. This max- "imum proportion is in any specific case eas ly found, being about as readi y determined by routine test as, for example, the proportion of sulfur permissible in steel for a particularpurpose. It is, however, always surprisingly small. In general with gelatino-silver-halid developing-out emulsions, it should be less than about 10 grains of active sensitizing compound, in 130 pounds of emulsion (the latter be ng computed as the weight of its non-aqueous, ingredients in the dry state);

or less than about 10 grains in 100 pounds sensitizing compound, to '100 pounds of gelatin (computed as dry) or 130 pounds of emulsion (computed as dry) iswithin the.

their physical properties. Consequently the use of my compounds provides a novel, dependable, and independent way for controlling the properties of photographic em'ul-v sions in addition to the customary expedients hitherto available. Gelatins, for instance, can be selected for their physical properties, such as setting ability, melting point and viscosity, without regard to whether they can be made into sufficiently lightsensitive emulsions, and any deficiency in sensitizing power can be made up by lncor orating a little quantity of one or more 0 my independent compounds. Nor are the grain-size characteristics affected by such additions of my compounds, they being independently controlled by the emulsion maker. In other WOI'dS,' I can establish a ratio of sensitizing compounds to silver halid in the emuls ons which is independent'of the ratio of gelatin to silver halid. Still differently stated, thesensitizer compounds can be added without adding any colloid, such, as gelatin, and are.

therefore, independent thereof.

My sensitizing compounds act as so-called chemical sensitizers instead of as optical sensitizers. In other words, they increase the eneral sensitiveness of photographic emulsions, notably developing-out ones, in which they are inc'orporated,that is to light of substantially the same wave lengths as those to which the emulsion would be sensitive without the incorporation of my compounds; instead of merely increasing the sensitiveness to some narrow roup of wave lengths. Unlike the effects of dyes, the sensitiveness is increased throughout the normal spectral range of the ,emulsioninstead (if at only those spectral points corresponding to the spectral absorption of the sensitizing compound. My compounds are effec-' tive in increasing. the general light-sensitiveness of orthochromatic, panchromatic,

X-ray, and all special emulsions, as well as .not specifically affect the dye action; but simply increase the general sensitiveness and thus increase the ordinary sensitiveness to tlue lightto at least as great an extent as to light of a color corresponding to the dye.

My sensitizing compounds may be used in many ways. Broadly they may be incorporated in emulsions or in colloids for emulsions or both. They can also enter the emulsion mixed with other ingredients thereof whether organic or inorganic. They may be added at different stages of emulsion manufacture, even when the latter is otherwise complete ready for coating. 'Since their action is rapid when incorporated, the coating in such case need be delayed only long enough to mix in the sensitizing compounds. With the grain characteristics, such as size distribution, etc., already determined, and the other physical and photographic properties of the emulsion alreadytaken care of at this stage, I'can practically independently increase its light-sensitiveness without impairing said other properties by adding one or more of my compounds. The latter are especially effective in emuls ons w iich are, at least slightly, alkaline.

Where different batches of emulsion, especially developing-out emulsions, fall below a required manufacturing standard of light sensitiveness, although they may be otherwise satisfactory, their sensitiveness can readily be brought up to standard by mixmg in my sensitizing compounds, the pro portion varying with the increase necessary to produce a uniform product. Emulsions having almost no practical light-sensitiveness but having enough other desirable qualities can be made usefully light-sensitive by my compounds. Thus the latter are useful in connection with emulsions having good initial light-sensitiveness and those having almost no initial sensitiveness. The increase in sensitiveness can be effected in one step by thoroughly stirring all of the sensitizing compound into the emulsion at one time; or it may be incor orated part at a time in successive steps. of emulsion from the same materials which have yielded deficient emulsions, correctional quantities of my sensitizing compounds can be premixed with an ingredient, such as gelatin.

The following example illustrates how light-sensitive photographic emulsions of the developing-out type may be prepared and improved by the aid of one or more of my hen making new batches sensitizing compounds. Of course, my lI1-"' vention is not -restricted to this illustration,

except as indicated in the claims. The emulsion-forming operations hereinafter 'described are along the lines of known practice, see for instance Die Photographic mit Brom'silber Gelatin by J. M. Eder, published in Halle, Germany in 1903 by Wilhelm Knapp as Part III of Eders Ausfuhrliches Handbuch der Photographie.

The two following solutions are made up, the parts being by weight:

A. 900 parts of silver nitrate in 9,200 parts of water.

B. 690 parts of potassium bromide and 50 parts of potassium iodidein 6,100 parts of water along with 300 parts of gelatin.

In mixing B, the halid salts are first dissolved, the water and the gelatin then added to the salt solution. Solution B is then warmed, say to 140 F. or 150 .F. for example; and the silver nitrate solution'A is gradually added to it with constant stirring. It is preferable to warm solution A before adding it to B, say to 150 F. or 160 F. for instance. When solution A has been thoroughly incorporated in solution B, there are then added 43 parts of strong ammonia previously dissolved in 900 parts of water. I Theemulsion formed bythese operations is allowed to stand for a short time, say 15 minutes to a half hour for example.

'Then 1050 parts of gelatin are dissolved in it with thorough mixing. The emulsion is next cooled, such, as by keeping in a cool space, until it sets to a firm jelly. The latter is broken up, as by shredding for instance, and thoroughly washed to remove soluble salts, such as potassium nitrate and any excess potassium halids. The wash water is, of course, cool enough not to melt the ieces of emulsion jelly. The washed emu sion is next remelted to 100 F. and 1050 parts of water soaked gelatin are thoroughly mixed into it, the temperature then being raised, say between 120 F. and

pared emulsion, they are most conveniently handled by dissolving them in a solvent which is inert with respectto the emulsion and simply acts as a vehicle to help in spreading the compounds throughout the emulsion, So long as an even distribution of the compounds throughout the emulsion is effected and the correct proportion of support, such as glass,

them .is added, their particular concentration in the solvent or vehicle is not important. It is ood ractice to keep the volume of the solution a ded to the emulsion under 2% of the volume. of the emulsion; but this ents) the emulsion is melted, the sensitizer dissolved in ethyl alcohol or water or a mixture of them, the volume of said solvent being under approximately 1.5% of the volume of the melted emulsion, and then the solution is thoroughly mixed into the emulsion. When necessary to minimize dilution, the volume of solution can be kept even below a fraction of 1%. I may mention also as very useful potassium selenocyanide.

lVith its light-sensitiveness increased by my compounds, the emulsion, beingmelted to the desired fiowabilit is coated on its 1m, paper, etc., in the well known way. It is convenient to control and check the process by coating samples of the emulsionbefore and after the addltion of my sensitizing compounds, the coated specimens being tried out photo graphically by any well known sensitometric test, or even by comparative camera exposures on the same subject under like conditions. Of course, the usual-precautions are observed during the emulsion making and coatin processes, such as the use of nonactinic or safe light, cleanness of vessels and air, etc. The different .gelatins sold for photo- 7 graphic emulsion-making may be used in the example iven above, hard ones-being very useful.

he temperatures given are, of

course, ad'usted if the particular gelatin employed as physical properties, such as 'melting and setting points, which deviate considerably from the usual ones, such adjustment being'a. matter of routine control.

Instead, however, of using gelatins which give emulsions of useful but. lower sensitiveness even before the addition of my sensitizing material, an almost inert gelatin may be employed,one which forms an emulsion which produces a developable image, if at i all, only after impractically long exposures, and then does not yield an image of desirable density. A gelatin which forms such a practically inert emulsion may be prepared in the way described under the head-, ing Preparation of ash-free gelatin in pages 1856 and 1859 of the Journal of the American Chemical Society,- September, 1922. Vol. XLIV, No. 9, being part of an article by Sheppard, Sweet, and Benedict on Elasticity of purified gelatin jellies as a function of hydrogen-ion concentration. Emulsions of impractically low light-sensitiveness made by the above described process from such prepared gelatin, are transformed by my sensitizing compounds into emulsions which give developable images of excellent density after usefully brief exposures. I have, for example, been able to increase the light-sensitivenessof some such low sensitive emulsions ten or even over twenty times, the exposures for a given subject in the latter case being cut to less than one twentieth of the original one and the image density being made excellent by a corresponding gain. Increases of the same general order of magnitude are made when my sensitizing compounds are added in similar proportions to emulsions which are made from normal photographic gelatins or mixtures of such normal gelatins with said al.- most inert gelatins, and already have useful, but lower initial sensitiveness. Difi'erent percentages of sensitizer produce correspondingly different increases. The increases in developing-out emulsions ap ear upon the usual developing operations. ustomary pyro and metolhydrochinon alkaline developers are suitable for example. Aninert emulsion prepared as above described is a very useful medium or standard in which to test the sensitizing properties of different compounds, a sample containing the comunsensitized emulsion,

Instead of the inert gelatin prepared according to the reference given in the preceding paragraph, I can prepare inert gelatins by treating active photographic gelatins with oxidizing agents. The latter oxidize the sulfur in the sensitizing substituted (allyl) thiocarbamide or corresponding carbimide, which occurs naturally in photographic gelatins, thus converting it to a non-sensitizing compound and leaving the gelatins practically inert. Dilute aqueous solutions of a peroxide, such as sodium peroxide (say from 5 to 10% by. weight) is intimately mixed into the elatin and then Washed out when the oxidatlon has occurred. The inert gelatin referred to in the preceding paragraph can be thus oxidized to make its inertness doubly sure.

When preparing inert gelatin on a considerable scale, it is far preferable to introduce the oxidizing step during the regular manufacturing operations, say the liming ing agents should be effective as desensi .tizers and yet not be present in quantities capable of materially reducing the yield of gelatin or harming its quality, especially its physical properties. Nor should they leave objectionable products from the oxidation reaction. For example, the regular liming solution of theusual gelatin manufacturing process can be saturated with as much calcium hypochlorite as will dissolve therein; or it can contain about to of sodium peroxide. Subsequent operations then proceed as usual.

' My sensitizing compounds may be incorporated into gelatin from which -photographic emulsions are to be made. This strengthened gelatin then constitutes a valuable intermediate in emulsion manufacture. While any good gelatin may be thus treated, that which has been rendered inert by the above described oxidation treat-v ment during liming or deliming is particularly adapted'to this strengthening. Emulsions made from the mixture have markedly increased light-sen-sitiveness as compared with those made from corresponding unstrengthened gelatins. The proportion of sensitizin material is, of course, adjusted'to give the esired control of the sensitiveness of emulsions made from the latin, the total. sensitizing material in the strengthened gelatin being thus brought to, or even above, norma 7 I When workin on a considerable scale, this activating 0% gelatin, such, for instance, as said inert gelat1n,is one of the most desir able ways of employing my sensitizing compounds. In fact, premixing ofone or more of my sensitizers wlth gelatin is my preferred system. During manufacture of the gelatin, say for instance whenthe concentrated gelatin solution comes from. theevaporator before setting and drying, -the sensitizing compound or compounds are added and thoroughly mixed to obtain effectively uniform distribution. For example 2 or 3 grains of any of the hereinabove listed compounds or mixtures of them is carefully mixed with each fraction of gelatin solution containin 100 pounds of gelatin (calcu-' lated as dry). The compound is taken up, preferably in as little aqueous-alcohol mixture as is practicable; and then this concen trated. solution addedto the gelatin solution. In this way undesirable dilution of the latter is avoided.

On a large sca1e,'the sensitizing solution may be accurately and continually dosed into a regulated stream of gelatin solution with continuous mixing. Alternativel dried or set gelatin may be allowed to swe in an aqueous. solution of the sensitizing compound. The. nearly uniform distribution or .difiusion of the compound in the gelatin thus efleted can be made even more nearly uniform by the swollen gelatin.

In the examples given above the steps of treating with ammonia and warming of the emulsion just before its final setting improve the photographic properties of the "emulsion, especially when the latter is made from hard elatins. But one or both of them melting and agitating may be omitted. In other words, my'sensitizing compounds act by themselves to increase the light-sensitiveness, whether ripening steps be employed or not, and so can Wholly or partially replace them. But I prefer to use themv because the efli'ect'of either or both of them is to help increase the light-sensitiveness of the emulsion and thus give a stronger initial sensitized condition which is multiplied or increased by using my sensitizing compounds. When using any of the inert gelatins mentioned above in making very sensitive emulsions, these steps can sometimes be shortened and made more cer tain in effect by reason of the use of my powerful and dependable sensitizing compounds.

I have describe elatin emulsions and emphasized the deveIoping-out and alkaline types because at the present time they are the ones which have the widest practical use. Moreover, they form the best medium "for testing new sensitizing-compounds. But other organic colloids and mixtures of them with'each other or with gelatin, wheretheir nature admits such mixtures, may be used in making light-sensitive emulsions which can be improved by adding my sensitizing material. Albumens, agar-agar, gums, such as gum-arabic, cellulosic derivatives such as collodion are instanced. While I have illustrated the use of m nection with such sensitive substances as silver bromide and silver iodide, other light-- sensitive substances can be employed, suchas silver chlorid, alone or mixed with one or more of the others. 1

Having thus described my invention, what I- claim as new and desire to secure by Letters Patent is:

1. A photographic developin -out emulsion comprising a colloid, partic es of photographic silver salt suspended therein, and an added compound therein upon which at least part of the light-sensitiveness of the emulsion depends, said compound containing a divalent selenium atom of the sulfur sensitizer in congroup directly joined by a double 'bond'to a single metalloid atom to which at least another group of'atoms is attached. the proportion of said compound being subsaid colloid.

' 2. A photographic developing-out emulsion comprising gelatin, particles of silver halid suspended therein and seleno carystantially independent of the proportion of 4. A photographic develo ing-out gela tino-silver-halld emulsion o the alkaline type of relatively .l 1igh-l ight-sensitiveness,

' sion comprising gplatin, particles of silver halid suspende erein and an added compound therein upon which at least art of the light-sensitiveness of the emuls on depends, said compound containing a divalent selenium atom irectly joined by a double bond to a single metalloid atom to which at least another group of atoms is attached, said emulsion being substantially free from 'sensitizin dye, and the pro ortion of said compoun being substantialy independent of the proportion of gelatin.

6. A photographic developing-out emulsion comprising gelatin, particles of photographic silver salt suspended therein and an added compound therein upon which at least part of the light-sensitiveness of the emulsion depends, said compound containing a divalent selenium atom of the sulfur group directly joined by a double bond to a single metalloid, atom to which at least another group .of atoms is attached, the

amount of added compound being less than the order of 10 grains per 130 ounds of emulsion and insufficient to cause immediate fo ging tendency.

In the process of preparing a developing-out gelatino-silver-halid emulsion, increasing the light-sensitiveness thereof by incorporating with the other constituents thereof a sensitizing compound containing a divalent selenium atom directly joined by a double bond to a single metalloid atom to which at leastanother group of atoms is attached. p

8. In the process of reparing a developing-out gelatino-silveralid emulsion, increasing the light-sensitiveness thereof by incorporating seleno carbamid with the other constituents thereof.

9. In the process of preparing 9. developing-out gelatino-silver-halid emulsion, increasing the light-sensitiveness thereof by incorporating allyl selenourea with the other constituents thereof.

10. In the process of preparing a developing-out gelatino-silver-halid emulsion of the alkaline type of relatively high lightsensitiveness, combining constituents of a gelatino-silver-halid emulsion of said type but of lower light-sensitiveness with an independent sensitizing compound, said compound containing a divalent selenium atom loid atom to which at least. another group of atoms is attached.

12. In the process of reparing a developing-out gelatino-silveralid emulsion, increasing the light-scnsitiveness thereof by incorporating with the other constituents thereof a sensitizing compound containin a divalent selenium atom directly joine by a double bond to a single metalloid atom to which at least another group of atoms is attached, the amount of said added compound being less than the order of 10 grains per 130 poundsof emulsion and insufficient to cause immediate fogging tendency.

13. An intermediate for use in making photographic emulsions, comprising an emulsion-forming colloid having incorporated therein a sensitizing compound containingja divalent selenium atom directly joined by a double bond to a single metalloid atom to which at least another group of atoms is attached.

14. An intermediate for use in making photographic emulsions, comprising gelatin having bamid. I

15. An intermediate for use in making photographic emulsions, comprising gelatin having incorporated therein allyl selenourea.

16. An intermediate for use in making photographic emulsions, comprising an emulsion-forming colloid having incorporated therein a sensitizing compound containing a divalent selenium atom directly joined by a double bond-to a single metalloid atom to Which at least another grou of atoms is attached, the amount of. sai added compound being less than the order of 10 grains in 100 pounds of gelatin.

17. The process ofmaking an intermediate for use in the preparation of photographic emulsions, which comprisesincon porating in an emulsion-forming colloid an independent sensitizing compound containing a divalent selenium atom directly joined by a double bond to a single metalloid atom to which at least another group of atoms is attached.

18. The process of making an intermediate for use in the preparation of photoincorporated therein seleno. cargraphic emulsions, which comprises incor porating in an emulsion-forming colloid a seleno carbamid.

19. The process of making an intermediate for use in the preparation of photographic emulsions, which comprises incorporating in an emulsion-forming colloid allyl selenourea,.

20. The process of making an intermediate for use in the preparation of photographic emulsions, which comprises incorporating in an emulsion-forming colloid an independent sensitizing compound containing a divalent selenium atom directly joined by a double bond to a single metalloid atom to which at least another group of atoms is attached, the amount of said added compound being less than the order of 10 grains per 100 pounds of said colloid (calculated as dry colloid) and being insufiicient to cause immediate fogging tendency.

21. The process of making an intermediate for use in the preparation-of photographic emulsions, which comprises incorporating in an emulsion-forming colloid a seleno carbamid, the amount of said added compound beingless than the order of 10 grains per 100 pounds of said colloid (calculated as dry colloid) and being insufiicient to cause immediate fogging tendency.

22. The process of making an intermediate for use in the preparation of photographic emulsions, which comprises incorporating in an emulsion-forming colloid allyl selenourea, the amount of said added compound being less than the order of 10 grains per 100 pounds of said colloid (calculated as dry colloid) and being insuflicient to cause immediate fogging tendency.

23. The process of making an intermediate for use in the preparation of photographic gelatino-silver-halid emulsions, which comprises substantially freeing gelatin from sensitizing compounds, and incorporating therein a sensitizing compound containing a divalent selenium atom directly joined by a double bond to a single metalloid atom to which at least another group of atoms is attached.

24. The process of making an intermediate for use in the pre aration of photographic gelatino-silveralid emulsions, which comprises substantially freeing gelatin from sensitizing compounds and incorporating therein seleno carbamid.

25. The process of making an intermediate for use in the pre aration of photogelatino-silveralid WhlCh comprises substantially freeing gelatin from sensitizing compounds, and incorporating therein a sensitizing compound containing a divalent selenium atom directly joined by a double bond to a single metalloid atom to which at least another grou of atoms is attached, the amount of sai added compound being less than the order of 10 grains for 100 pounds of gelatin (calculated as dry gelatin), and being insufiicient to cause immediate fogging tendency in emulsions made from said intermediate. Signed at Rochester, New York this 18th day of January 1926. i

S L E. SHEPPARD.

emulsions, I 

